In a production process of a yarn comprising a bundle of numerous continuous filaments such as synthetic fibers, there is a case where fluffs or fuzz occur on the yarn owing to broken filaments and the like. Further, owing to broken filaments and the like, it can happen that filaments may come off from the yarn, to decrease the number of filaments constituting the yarn or to cause yarn splitting. Moreover, it can happen that all the filaments constituting the yarn may be broken to cut the yarn. Most of these defects (disorders) occurring on the yarn are caused by external or internal structural changes of the yarn based on variations of various process conditions such as the variations of tension and heat treatment temperature in the production process. Moreover, fluffs or fuzz once separated from the yarn and suspended in air may reattach to the yarn in the production process of the yarn.
These defects of yarns greatly affect the quality of yarns themselves and the quality of textile products formed of the yarns. Therefore, it is very important for quality control of yarns themselves and textile products, to accurately detect and identify the defects of yarns. In addition, if the states of the yarns running in a yarn production process can be constantly monitored to early identify the changes in the states of yarns or frequent occurrences of defects caused by the variations of process conditions, the yield in the yarn production process can be enhanced. That is, it is important to identify the defects of running yarns online.
Most of yarn production processes employ a method in which multiple yarns are made to run in parallel to each other for simultaneous production of multiple yarns. In such a production process, it is important for quality control of produced yarns themselves and of yarn package obtained by winding the produced yarns that the multiple yarns running in parallel to each other are simultaneously inspected and that the defects of every yarn are detected for obtaining the information on the defects of every yarn.
As a traditional method for constantly monitoring the state of a yarn for detecting the defects occurring on the yarn, proposed is a method in which an inspection region larger than the width of a yarn is irradiated with the light from a light projecting section, so that a light receiving section may detect the light intensity transmitted or reflected when the running yarn passes through the inspection region, for detecting the defects occurring on the yarn in reference to the changes of light intensity (see Patent Literature 1). However, the inspection method described in Patent Literature 1 requires at least one light receiving section for one yarn. For example, in a process for simultaneously producing 100 yarns, 100 light receiving sections are necessary. Therefore, this inspection method is very costly for inspecting all yarns.
As a method for inspecting the defects of multiple yarns simultaneously at low cost, proposed is a method in which a light projecting means is set up on one lateral side of the yarns while a light receiving means is set up on the other side beyond the yarns, with the yarns placed inside of, immediately above or immediately below the luminous flux, to detect each fuzz formed on a yarn when the fuzz intercepts the light (see Patent Literature 2). However, according to the inspection method described in Patent Literature 2, which of the yarns placed between the light projecting means and the light receiving means has been found to have a defect cannot be determined. Therefore, the information on the defects of every yarn cannot be obtained. Further, in the case where a flat defect thinly spreads over the surface of a yarn, since the quantity of intercepted light is small, it is difficult to detect such a defect by this inspection method.
As a method for inspecting the defects of yarns in a yarn sheet in which numerous yarns are laid out parallel to each other, proposed is a method in which the yarns are imaged using a camera to detect the defects of the yarns by image processing (see Patent Literature 3). However, according to the inspection method described in Patent Literature 3, the number of yarns that can be inspected simultaneously is small due to the difficulty of the resolution in the width direction of the camera. For example, it is difficult to simultaneously inspect about 100 yarns running in parallel to each other, and further in the case where the multiple yarns are inspected simultaneously, the yarns found to have defects cannot be identified, not allowing the information on the defects of every yarn to be obtained.
Patent Literature 1: JP 7-300280 A
Patent Literature 2: JP 61-114115 A
Patent Literature 3: JP 2004-277938 A